Acetabular implant for hip prosthesis

ABSTRACT

An acetubular implant includes a cup for receiving an insert freely articulated in the cup, equipped with iliac expansions ( 8 ) and a plugging element; the cup consists of a hemispherical part extended by a cylindrical part whereto are attached the iliac expansions. The cylindrical part extends over substantially a half circumference of an equatorial edge of the hemispherical part and is defined by a plane (R) inclined on the equatorial plane. Part of the outer surface of the cup ( 2 ) is covered with a macrostructure ( 24 ) defining a set of raised parts with a series of equatorial and meridian grooves of predetermined shape such that the macrostructure is neither too rough nor too smooth.

CROSS REFERENCE TO RELATED APPLICATION

This is the 35 USC 371 national stage of International ApplicationPCT/FR00/02657 filed on Sep. 26, 2000, which designated the UnitedStates of America.

FIELD OF THE INVENTION

The present invention relates to an acetabular implant for a hipprosthesis, of the type comprising a cup which is designed to receive aninsert freely articulated in the cup, and which is equipped with iliacextensions and with an obturator element for bone fixation.

This implant is for first intention use and also for revision, that isto say it can be put into place not only the first time, but also if thebone cavity needs to be altered or improved, in other words if thepathology causes bone defects to appear which require grafts of moderatesize. In other words, this implant can be used for revision as long asthe cotyloid cavity has not been destroyed by more than 50%.

BACKGROUND OF THE INVENTION

French patent 93.12.097 (2,710,836) describes an acetabular implant ofthis type for a total hip prosthesis in which the cup has a sphericalshape, which is the geometry generally used for such implants. However,such a configuration is not particularly well adapted to the anatomy ofthe acetabular cavity of a hip, the upper wall of which protrudesfarther than the lower wall. The result of this is a mechanicalstability which leaves something to be desired.

In addition, in the known implants, the iliac tabs generally include arectilinear part directly attached to the opening edge of the cup. Theresult of this is a lack of adaptation to the anatomy at this site, inparticular to the cotyloid brow, which is likely to affect the properanchoring of the prosthesis.

A great many known implants have a cup with a smooth surface in contactwith the wall of the cotyloid cavity, sometimes equipped with anchoringpoints, so that their mechanical stability may become compromised in thelong term. To remedy these shortcomings, it has been proposed, forexample, to perforate the wall of the cotyloid cavity (U.S. Pat. No.3,740,769, Gierman patent 3,205,526). However, experience has shown thatthese provisions are not entirely satisfactory.

SUMMARY OF THE INVENTION

The object of the invention is therefore to make available an acetabularimplant designed in such a way as to afford it excellent fixation duringand after surgery, both in the medium term and in the long term.

According to the invention, the cup consists of a hemispherical part towhich the obturator element is fixed and which is continued by acylindrical part to which the iliac extensions are fixed.

Thus, the cylindrical part, whose width and angular extent are suitablydetermined, continues the cup in the zone of the iliac extensions, thatis to say in the upper part of the cotyloid cavity. This cylindricalpart is thus in contact with the bone wall as far as the edge of theacetabular cavity, with which it ensures better contact than a simplyhemispherical cup. In other words, the upper part of the implant closelycovers the bone wall, which considerably reduces the risk of dislocationin the extreme angular positions of the associated femoral stem and ofthe insert articulated in the cup.

According to an advantageous embodiment of the invention, thecylindrical part extends over substantially a half-circumference of anequatorial edge of the hemispherical part and is delimited by a planeinclined on the equatorial plane of the hemispherical part, thisinclined plane continuing beyond the cylindrical part via a truncatededge of the hemispherical part situated in the same inclined plane.

The advantage of the truncation of the spherical part thus realized inthe lower zone of the implant lies in the fact that, in the extremeposition of the insert in internal flexion-rotation or in externalextension-rotation, it prevents the escape of the insert from the cup bya cam effect. This is because the neck of the femoral stem can no longercome into abutment on the lower opening edge of the cup and thereby riskexpulsion of the insert.

In the extreme flexion position, the neck of the femoral stem does notrisk coming into abutment against the cylindrical part of the cup, thewidth of which is suitably chosen for this purpose.

Indeed, this geometry of the acetabular implant greatly reduces the riskof dislocation in the two opposite extreme positions of the insert andof the associated femoral stem, while at the same time promotingexcellent angular clearance. Moreover, the geometry of the cup enablesit to make maximum provision for the anatomy of the acetabular cavity.

According to another characteristic of the invention, the iliacextensions comprise a rectilinear end attached to the edge of the cup,continued by a curved part whose curvature is adapted to the cotyloidbrow of an acetabular cavity, a rectilinear part and then an incurvedpart continuing said curved part; lastly, a final rectilinear part whichis attached to the incurved part and in which a hole is formed forpassage of a bone anchoring screw.

Advantageously, the two extreme rectilinear parts delimit betweenthemselves an angle of about 45 degrees preferably.

This geometry allows the iliac extensions to adapt closely to the boneanatomy at this site, near the edge of the acetabular cavity, which edgeis itself modeled if necessary.

According to another particular feature of the invention, amacrostructure with raised parts promoting primary anchoring and boneintegration is machined on the outer surface of the cup situatedsubstantially between said inclined plane delimiting the opening of thecup and a spherical cap delimiting the bottom of the cup, and thismacrostructure and the cap are coated with calcium hydroxyapatite.

This macrostructure, the geometry of which is suitably chosen so as tobe neither too smooth nor too rough, permits better primary andlong-term anchoring of the cup by means of bone regrowth, thereby givingthe implant its long-term stability.

BRIEF DESCRIPTION OF THE DRAWINGS

Other particular features and advantages of the invention will becomeevident from the following description in which reference is made to theattached drawings which show a nonlimiting illustrative embodiment ofthe invention.

FIG. 1 is a side elevation, substantially to scale, of an embodiment ofthe acetabular implant according to the invention, viewed in a sagittalplane.

FIG. 2 is an elevation, in a frontal plane, of the implant in FIG. 1.

FIG. 3 is an elevation, on an enlarged scale compared to FIGS. 1 and 2,of an industrial embodiment of the implant according to the invention.

FIG. 4 is an elevation along the arrow K in FIG. 3.

FIG. 5 is an elevation of the acetabular implant in the direction of thearrow K in FIG. 3.

FIG. 6 is a sectional view along 6—6 in FIG. 3.

FIG. 7 is a perspective view, on an enlarged scale, of a detail of theouter surface, with macrostructure, of the implant in FIGS. 3 to 6.

FIG. 8 is a partial sectional view, on an enlarged scale, of equatorialgrooves visible in FIGS. 3 to 6.

FIG. 9 is an elevation, on an enlarged scale, of an embodiment of aniliac extension attached to an implant according to one of FIGS. 1 to 7.

FIG. 10 is a side elevation of the iliac extension in FIG. 9.

FIG. 11 is a perspective view of the iliac extension in FIGS. 9 and 10.

FIG. 12 is an elevation, in a frontal plane, of the implant according tothe invention and of the upper end of the associated femoral stem, shownin abduction-extension.

FIG. 13 is an elevation analogous to FIG. 12, showing the extremeposition which the femoral stem can adopt in relation to the acetabularimplant in adduction-flexion.

DETAILED DESCRIPTION OF THE INVENTION

The acetabular implant 1 illustrated in the drawings is intended for atotal hip prosthesis, of which only the proximal part 5 of the femoralstem has been shown in FIGS. 12 and 13.

The implant 1 comprises a cup 2 designed to receive an insert 3 which isfreely articulated in the cup and into which it is possible to introducea head (FIGS. 12 and 13) attached to the end of the neck of the proximalpart 5.

The cup 2 consists of a hemispherical part 6 delimited by an equatorialplane P (FIG. 1) and continued by a cylindrical part 7 to which twoiliac “extensions” 8 are fixed. At the opposite end from these, anobturator element 9 formed by a hook is attached to the lower openingedge of the hemispherical part 6 of the cup 2, at a positiondiametrically opposite to a point situated at the center of an intervalbetween the extensions 8.

The cylindrical part 7 extends beyond the equatorial plane P, over apart of the circumference of the opening edge of the cup 2, namely oversubstantially a half-circumference. To be more precise, the cylindricalpart 7 in fact extends over an angular sector substantially greater thana half-circumference. It will be seen in FIG. 1 that this part 7 isdelimited by a plane R which is inclined on the equatorial plane P andwhich continues beyond the cylindrical part 7 via a truncated edge 11 ofthe hemispherical part 6, this truncated edge 11 being situated in thesame inclined plane R. A sort of truncation of the hemispherical part 6is thus formed, extending from the intersection I between the inclinedplane R and the equatorial plane P to the lower edge of the cup 2 and tothe obturator element 9.

In the radial direction, the cylindrical part 7 has a width 1appropriate to the anatomy of the cotyloid cavity, and the plane Rdelimits with the equatorial plane P an angle A of about 15 degrees, thesummit of which is the intersection I. The inclined plane R intersectsthe equatorial plane P between the center O of the hemispherical part 6and its edge contiguous to the obturator element 9.

The outer edge of the cylindrical part 7 is truncated in such a way asto delimit a bevel 12 which extends parallel to the equatorial plane Pand on which the iliac extensions 8 are fixed.

Each iliac extension 8 can be adapted to the individual bone surface. Itcomprises a rectilinear end 13 attached to the edge of the cup 2,continued by a curved part 14 whose curvature is adapted to the cotyloidbrow 15 of an acetabular cavity (FIG. 12), a rectilinear part 16 andthen a second incurved part 17 (FIGS. 9 to 11) continuing said curvedpart 16; lastly, each extension 8 terminates in a final rectilinear part18 in which a hole 19, advantageously of oblong shape, is formed forpassage of an optional bone anchoring screw 21 (FIG. 12).

The final rectilinear part 18 is advantageously inclined by about 45degrees on the initial rectilinear part 13 while the intermediaterectilinear part 16 can be inclined by about 15 degrees on theperpendicular to the part 13. The oblong hole 19 is advantageouslyequipped with a countersink 22 on its circumference, permitting multipleorientation of the anchoring screw 21.

The curvature of the incurved part 14, adapted for the passage of thecotyloid brow, and the angulation of the rectilinear part 18 at 45degrees in relation to the tab 13 guarantee the proximity between theextensions 8 and the bone surface. Thus, these two particular featuresensure excellent respect of the local anatomy by the iliac extensions 8.

A macrostructure 24 with raised parts 28 is machined on a part of theouter surface of the cup 2. This part covered by the miacrostructure 24is delimited substantially by the opening edge 10 of the cup 2 and aspherical cap 25 forming the bottom of the cup 2. This macrostructure 24and the cap 25 are coated with a layer of calcium hydroxyapatite whichcontributes, along with the macrostructure 24, to bone regrowth and boneintegration.

The macrostructure 24 is separated from the free edge 10 of the cup 2 bya smooth band 26 of small width. The macrostructure 24 delimits a set ofequatorial grooves 26 situated in equatorial planes parallel to theplane P, and a set of meridian grooves 27 perpendicular to theequatorial grooves 26. This assembly of grooves 26 and 27 thus forms asort of gridiron delimiting, at the intersections between the grooves 26and 27 whose cross sections have a V-shaped profile (FIGS. 3 to 8), aseries of raised parts 28 each having a rectangular base.

The flanks 26 a of the equatorial grooves 26 can be inclinedadvantageously Abut without implying any limitation) by an angle B ofabout 30 degrees on a median plane M passing through the base of eachgroove 26, whose angle of opening is thus 60 degrees and whose depth canbe about 1 mm, for example.

The same applies to the flanks 27 a of the meridian grooves 27 (FIG. 7).Moreover, and again by way of a nonlimiting numerical example, theridges forming the bottom of the equatorial grooves 26 can be spacedapart by an interval e of about 2 mm (FIGS. 6 and 8), the number ofthese equatorial grooves 26 varying with the size of the cup 2.

Finally, the meridian grooves 27 are spaced apart in pairs by an angleof advantageously about 6 degrees (FIG. 7) so that their total number onthe circumference of the cup 2 is 60. This total number is constantirrespective of the size of the cup.

It will be seen from FIGS. 3 and 7 that each of the raised parts 28 hastransverse and longitudinal profiles whose transverse flanks 28 adelimit equatorial grooves 26, while their longitudinal flanks 28 bdelimit meridian grooves 27. All these flanks are joined to a flat face28 c.

The cup 2, which is not cemented, can be made, for example, of stainlesssteel of standard ISO 53 32-1, covered with calcium hydroxyapatite(CHA).

The acetabular implant 1 which has just been described is put into placein the manner shown in FIG. 12: its dimensions are chosen so that thediameter of the cup 2 is slightly greater than the diameter of thenatural cotyloid cavity in which it is to be implanted by means of apress fit, that is to say by impaction. At the same time, the iliacextensions 8 take up their position straddling the cotyloid brow 15,while the obturator element 9 is introduced into the obturator foramen20. If necessary, the screws 21 are implanted through the holes 19 inthe appropriate orientation to find the best bone anchoring, whichscrews 21 can be of the spongy bone type or of the cortical bone type.

The immediate stability of the cup 2, during and after surgery, isensured by the combination of the following elements:

the press-fit impaction of the implant 1 in the natural cotyloid cavity,

the presence of the macrostructure 24 coated with hydroxyapatite,

the (optional) screwing of the iliac extensions with the screws 21,

the positioning and securing of the cup 2 by the obturator element 9.

The stability of the implant in the medium and long term is obtained bythe osseoconduction induced by the calcium hydroxyapatite coating, bythe osseointegration at the heart of the macrostructure 24 and,possibly, by the action of the iliac extensions 8 and of the obturatorelement 9.

Thus, all these elements guarantee excellent primary and secondaryfixation of the implant 1 and, consequently, an optimum lifetime.

The iliac extensions 8 adaptable to the bone, whose surface they match,and the obturator element 9 permit gripping of the ischiopubic branch.

The presence of the smooth band 30 avoids indentation of the equatorialplane P by the edge of the macrostructure 24. Moreover, the numericalvalues indicated above, although nonlimiting, have proven, in tests, toprovide the most advantageous results in terms of improving the efficacyof the primary and long-term secondary fixation of the implant. Thus,the fact that the total number of meridian grooves 28 is limited to 60irrespective of the size of the acetabular implant means that it ispossible, for large sizes, to form large gridirons which have largeraised parts 28 and which promote attachment to the bone wall. Themacrostructure 24 is advantageously machined on the cup 2, and not addedto it, as this has proven more effective in terms of osseointegration.

Moreover, it has been found that there is no point in arranging amacrostructure 24 on the spherical cap 25 which comes into contact withthe bottom of the natural cotyloid cavity. This is because the stressesacting at this level are low, whereas they are at their greatest in theupper zone of the cotyloid cavity, the forces exerted diminishing in theposterior and anterior zones of the cavity.

In summary, the geometry of the cup 2, hemispherical and surmounted by acylindrical part 7, with truncation at 15 degrees through the plane R,permits excellent angular clearance as far as the limit positions andavoids the risks of dislocation in these extreme positions, while at thesame time also respecting the anatomy of the acetabular cavity to thegreatest possible extent.

The geometry of the iliac extensions 8 ensures their optimal contactwith the bone surface, in particular by virtue of the bend on theseextensions at the level of their incurved part 14.

The combination of the macrostructure 24, whose geometry is welldefined, as has been explained above, and of a coating of calciumhydroxyapatite ensures, on the one hand, good penetration of the bonetrabeculae within the macrostructure 24, that is to say promotes goodosseointegration, and, on the other hand, guarantees the stability ofthe acetabular implant over the course of time.

The invention is not limited to the described embodiments and caninclude numerous alternatives. Thus, the dimensions and the geometry ofthe raised parts 28 defined by the macrostructure 24 could differsubstantially from the example described, likewise the inclination of,for example, the plane R on the equatorial plane P.

What is claimed is:
 1. An acetabular implant (1) for a hip prosthesis,comprising a cup (2) which is designed to receive an insert (3) freelyarticulated in the cup, and which is equipped with iliac extensions (8)and with an obturator element (9) for bone anchoring, which cupcomprises a hemispherical part (6) to which the obturator element (9) isfixed and which is continued by a cylindrical part (7) to which theiliac extensions (8) are fixed, wherein said cylindrical part (7)extends over substantially a half-circumference of an equatorial edge ofthe hemispherical part (6) and is delimited by a plane R inclined on theequatorial plane (P) of the hemispherical part (6), the inclined planecontinuing beyond the cylindrical part (7) via a truncated edge (11) ofthe hemispherical part (6) situated in the same inclined plane (R). 2.The implant as claimed in claim 1, wherein said inclined plane (R)delimits, with the equatorial plane (P) of the cup (2), an angle (A) ofabout 15 degrees, which intersects the equatorial plane between thecenter (O) of the hemispherical part (6) and its edge contiguous to theobturator element (9), the cylindrical part (7) having a width (1)appropriate to this purpose.
 3. The implant as claimed in claim 1,wherein the iliac extensions (8) comprise a rectilinear end (13)attached to the edge of the cup (2), continued by a curved part (14)whose curvature is adapted to the cotyloid brow (15) of an acetabularcavity, a rectilinear part (16) and then an incurved part (17)continuing said curved part, and lastly a final rectilinear part (18)which is attached to the incurved part and in which a hole (19) isformed for passage of a bone anchoring screw (21).
 4. The implant asclaimed in claim 3, wherein the final rectilinear part (18) is inclinedby about 45 degrees on said rectilinear end (13), the hole (19) isoblong and comprises a countersink (22) permitting multiple orientationof the bone anchoring screw (21).
 5. The implant as claimed in claim 1,wherein a macrostructure (24) with raised parts (28) promoting boneintegration is machined on the outer surface of the cup (2) situatedsubstantially between said inclined plane (R) delimiting the opening ofthe cup (2) and a spherical cap (25) delimiting the bottom of the cup,and the macrostructure and the spherical cap are coated with calciumhydroxyapatite.
 6. The implant as claimed in claim 5, wherein a smoothband (30) is reserved between an opening edge (10) of the cup (2) andthe start of the macrostructure (24) with raised parts (28).
 7. Theimplant as claimed in claim 6, wherein the macrostructure (24) delimitsa set of equatorial grooves (26), situated in parallel equatorialplanes, and a set of meridian grooves (27) perpendicular to theequatorial grooves, and the different equatorial and meridian grooveshave a V-shaped cross section whose flanks (26 a) are inclined by about30 degrees on a median plane (M) passing through the bottom of thegroove (26, 27), while the depth of these equatorial and meridiangrooves is about 1 mm.
 8. The implant as claimed in claim 7, wherein thebottom of the equatorial grooves forms ridges (26), which are spacedapart by about 2 mm and the number of these grooves varies with the sizeof the cup (2).
 9. The implant as claimed in claim 7, wherein themeridian grooves (27) are spaced apart in pairs by an angle of about 6degrees so that their total number on the circumference of the cup (2)is 60, said total number being constant irrespective of the size of thecup.